Graphene is a single planar sheet of sp2 bonded carbon atoms. This two-dimensional structure provides the building block for the formation of three-dimensional graphite, one-dimensional nanotubes, and fullerenes (or “bucky balls.”) Graphene is predicted to have remarkable physical properties, including large thermal conductivity as compared to the in-plane value of graphite, superior mechanical properties, and excellent electronic transport properties. Furthermore, the charge carriers in graphene are predicted to have zero effective mass, and the transport properties are expected to be governed by the relativistic Dirac equation rather than the Schrödinger equation.
Mechanical cleavage has been widely used to separate a few layers of graphene from highly oriented pyrolytic graphite (HOPG). Ribbons and terraces with step edges of graphene have been obtained by peeling off the surface layers of HOPG using scotch tape. Alternative methods, such as exfoliation and epitaxial growth on single-crystal silicon carbide substrates, have produced multilayer graphene sheets, but not single layer graphene sheets. In any event, known methods of producing graphene sheets are tedious and labor-intensive. Furthermore, none of the known methods address how to place the graphene sheets in a desired location, which is of great importance in constructing electrical experiments and assembling heterogeneous electronic systems.